Metallic and semiconducting carbon nanotube sorting

ABSTRACT

A method of printing an electronic device includes providing a source of a mixture of semiconducting carbon nanotubes and metallic carbon nanotubes in a carrier liquid, a printhead, and a substrate. The mixture of semiconducting carbon nanotubes and metallic carbon nanotubes in the carrier liquid is separated using the printhead. One of the separated semiconducting carbon nanotubes and the separated metallic carbon nanotubes is caused to contact the substrate in predetermined pattern.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned, U.S. patent application Ser. No.______ (Docket K000816), entitled “METALLIC AND SEMICONDUCTING CARBONNANOTUBE SORTING”, filed concurrently herewith.

FIELD OF THE INVENTION

This invention relates generally to sorting of nanomaterials, and inparticularly to separating semiconducting carbon nanotubes and metalliccarbon nanotubes.

BACKGROUND OF THE INVENTION

A single-wall carbon nanotube (SWNT) is a cylindrical structure formedby rolling up a graphene sheet. The direction and magnitude of therolling vector define the chirality and diameter, respectively, of theresulting nanotube and determine whether the nanotube is metallic orsemiconducting. Common methods used to synthesize SWNT produce complexmixtures that contain many chiralities. Statistically, one third of themixture is metallic while the remaining mixture is semiconducting.However, many applications of SWNTs, such as conductive films andhigh-performance field-effect transistors, require enrichment ofnanotubes with metallic and semiconducting properties, respectively.Consequently, there have been intense efforts to develop various sortingtechniques for separating SWNTs, including selective chemistry,dielectrophoresis, selective oxidation, ultracentrifugation and DNAwrapping chromatography. Several of these methods have been demonstratedto achieve high-purity separation of metallic and semiconducting SWNTs.However, these methods suffer from problems including low yield or highcost.

Carbon nanotubes have been separated by both physical (electrophoresisand centrifugation) and chemical methods (chromatography, selectivesolubilization and selective reaction). Electrophoresis has beenemployed for separating various kinds of SWNTs, synthesized by laservaporization, arc discharge, chemical vapor deposition (CVD) and HiPco(high pressure CO) process, according mainly to electrical property(metallic/semiconducting) together with length and diameter. Chargedbiological macromolecules are commonly separated by electrophoresisusing gel in an electric field. In order to process SWNTs in the gel,however, the SWNTs have to be individually dispersed with aid ofsurfactant such as sodium dodecylsulfonate (SDS), sodium cholate (SC)and sodium dodecylbenzenesulfonate (SDBS). This type ofmetallic/semiconducting separation utilizes different polarizablecharacters between the nanotubes under an electric field.Dielectrophoresis technique was first used for the alignment andpurification of SWNT bundles in isopropyl alcohol and has been extendedto separation of individually dispersed SWNTs.

Sodium dodecyl sulphate (SDS) and/or sodium cholate (SC) have beencommonly used as detergents to dissolve SWNTs. In 2005, Arnold andHersam disclosed, in Nature Nanotechnology, 1, 60-65 (2006), an exampleof density gradient ultracentrifugation (DGU) for separation of thediameter of SWNTs. They used structure discriminating surfactants andapplied the DGU to separate metallic/semiconducting nanotubes.

Covalent and non-covalent sidewall chemistries to selectively impartionic character to metallic or semiconducting carbon nanotubes also havebeen developed. For example, Woo-Jae Kim et al. disclose in Chemistry ofMaterials, 19, 1571-1576 (2007), that selective covalent sidewallfunctionalization of metallic SWNTs can be achieved withp-hydroxybenzene diazonium salt after which a negative charge can beinduced on the metallic SWNTs through deprotonation in alkalinesolutions, thus enabling subsequent separation by electronic type usingfree solution electrophoresis.

In US Patent Publication No. 2010/0101983A1, Butler et al. describe aflow sorting method of detecting and separating carbon nanotubes basedon a electrophoretic method. In particular, the method involves focusingthe dispersion of individually suspended carbon nanotubes into a singlefile stream in a microfluidic device, and detecting and sorting ofmetallic and semiconducting nanotubes.

Each of these techniques, however, is disadvantaged in that they are notreadily scalable, suffer from low yield, or are expensive. There isclearly a need, therefore, for efficiently sorting semiconducting andmetallic nanotubes using a scalable, high yield, or low cost technique.

SUMMARY OF THE INVENTION

According to one aspect of the invention, separation of semiconductingand metallic nanotubes using a continuous inkjet system that includeselectrostatic deflection is provided. Ionic side-groups are selectivelyattached on metallic nanotubes and concentrated in a drop that can bedeflected using a deflection electrode of an electrostatic deflectionmechanism. The present invention provides a fast and efficient way tosort metallic and semiconducting nanotubes. When compared toconventional techniques, the present invention reduces the need fordetection and does not require a single file stream of nanotubes, thusmaking the present invention more efficient and scalable.

One example embodiment of the present invention provides a system andmethod for separating metallic SWNTs from semiconducting SWNTs or viceversa to obtain a purified batch of semiconducting SWNTs or metallicSWNTs that has higher yield of the desired product, and is moreefficient and scalable when compared to conventions systems and methods.The method includes selectively functionalizing metallic SWNTs withcharged functional groups in a mixture containing metallic andsemiconducting SWNTs such that the metallic SWNTs carry a net charge andforming a dispersion of this mixture in a fluid such that the metallicand semiconducting SWNTs are suspended in this fluid in a stabledispersion. The metallic SWNTs are enriched by sending the mixturethrough an inkjet printing system and applying an electric field toselectively attract functionalized metallic SWNTs in a drop. The dropenriched with functionalized metallic SWNTs is the separated from otherdrops, for example, by deflecting the drop using a deflection mechanism.In another embodiment of the present invention, semiconducting SWNTs arefunctionalized to have a net charge, are enriched, and then separatedfrom other drops.

According to another aspect of the present invention, a method ofprinting an electronic device includes providing a source of a mixtureof semiconducting carbon nanotubes and metallic carbon nanotubes in acarrier liquid, a printhead, and a substrate. The mixture ofsemiconducting carbon nanotubes and metallic carbon nanotubes in thecarrier liquid is separated using the printhead. One of the separatedsemiconducting carbon nanotubes and the separated metallic carbonnanotubes is caused to contact the substrate in predetermined pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiments of theinvention presented below, reference is made to the accompanyingdrawings, in which:

FIG. 1 illustrates different ways to roll up a graphene sheet to obtaincarbon nanotubes with different chiralities;

FIGS. 2A and 2B illustrate examples of differential functionalization ofsemiconducting nanotubes and metallic nanotubes, respectively;

FIG. 3 is a block diagram of an example embodiment of a carbon nanotubesseparation system of the present invention;

FIG. 4 is a schematic diagram of an example embodiment of the presentinvention;

FIG. 5 is a schematic diagram of an example embodiment of the presentinvention showing drops traveling in air after being formed from aliquid jet of a nozzle of a printhead of the present invention;

FIGS. 6A and 6B illustrates jets of a mixture of semiconducting carbonnanotubes and metallic carbon nanotubes in a carrier liquid, with one ofthe jets, as shown in FIG. 6A, being functionalized to carry a chargewithout voltage being applied to an adjacent charge electrode, and oneof the jets, as shown in FIG. 6B, being functionalized to carry a chargewith voltage applied to an adjacent charge electrode; and

FIG. 7 is a flowchart outlining the method steps of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elementsforming part of, or cooperating more directly with, apparatus inaccordance with the present invention. It is to be understood thatelements not specifically shown or described may take various forms wellknown to those skilled in the art. In the following description anddrawings, identical reference numerals have been used, where possible,to designate identical elements.

The example embodiments of the present invention are illustratedschematically and not to scale for the sake of clarity. One of theordinary skills in the art will be able to readily determine thespecific size and interconnections of the elements of the exampleembodiments of the present invention.

Throughout the specification and claims, the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise. The meaning of “a,” “an,” and “the” includes pluralreference, the meaning of “in” includes “in” and “on.” Additionally,directional terms such as “on”, “over”, “top”, “bottom”, “left”, “right”are used with reference to the orientation of the Figure(s) beingdescribed. Because components of embodiments of the present inventioncan be positioned in a number of different orientations, the directionalterminology is used for purposes of illustration only and is in no waylimiting.

As described herein, example embodiments of the present inventionprovide a printing system, a printhead, a printhead component(s), orprinting methods typically used in inkjet printing systems. In suchsystems, the liquid is an ink for printing on a recording media. Thepresent invention, however, other applications are emerging, which useinkjet print heads to emit liquids (other than inks) that need to befinely metered or deposited with high spatial resolution. The presentinvention includes an inkjet printing system, printhead, and printheadcomponents to separate semiconducting and metallic nanotubes. As such,as described herein, the terms “liquid” and “ink” refer to any material,for example, semiconducting and metallic nanotubes, that can be ejectedby the printing system, printhead, or printhead components of thepresent invention described below.

Continuous inkjet (CIJ) drop generators rely on the physics of anunconstrained fluid jet, first analyzed in two dimensions by F. R. S.(Lord) Rayleigh, “Instability of Jets,” Proc. London Math. Soc. 10 (4),published in 1878. Lord Rayleigh's analysis showed that liquid underpressure, P, will stream out of a hole, the nozzle, forming a liquid jetof diameter d_(j), moving at a velocity v_(j). The jet diameter d_(j) isapproximately equal to the effective nozzle diameter d_(n) and the jetvelocity is proportional to the square root of the reservoir pressure P.Rayleigh's analysis showed that the jet will naturally break up intodrops of varying sizes based on surface waves that have wavelengths λlonger than πd_(j), i.e. λ≧πd_(j). Rayleigh's analysis also showed thatparticular surface wavelengths would become dominate if initiated at alarge enough magnitude, thereby “stimulating” the jet to producemono-sized drops.

Continuous inkjet (CIJ) drop generators employ a periodic physicalprocess, a so-called “perturbation” or “stimulation” that has the effectof establishing a particular, dominate surface wave on the jet. Thestimulation results in the break off of the jet into mono-sized dropssynchronized to the fundamental frequency of the perturbation. It hasbeen shown that the maximum efficiency of jet break off occurs at anoptimum frequency F_(opt) which results in the shortest time to breakoff. At the optimum frequency F_(opt) the perturbation wavelength λ isapproximately equal to 4.5d_(j). The frequency at which the perturbationwavelength λ is equal to πd_(j) is called the Rayleigh cutoff frequencyF_(R), since perturbations of the liquid jet at frequencies higher thanthe cutoff frequency won't grow to cause a drop to be formed. The dropstream that results from applying Rayleigh stimulation will be referredto herein as a stream of drops of predetermined volume.

The example embodiments of the present invention discussed below withreference to FIGS. 1-6 are described using particular combinations ofcomponents, for example, particular combinations of drop chargingstructures, drop deflection structures, drop catching structures, dropformation devices, also called stimulation devices, and drop velocitymodulating devices. It should be understood that these combinations ofcomponents are interchangeable and that other combinations of thesecomponents are within the scope of the invention.

The system of nomenclature for single walled carbon nanotubes (SWNTs) isillustrated in FIG. 1. The structure of single-wall carbon nanotube(SWNT) 10 can be described as atomically thin tubes formed by rolling upa graphene sheet 11. The properties of SWNTs are determined by thealignment of the hexagons with respect to the tube axis. Since a SWNT 10can be prepared by rolling up a graphene sheet 11 into a seamlesscylinder, the structure is defined by a roll-up vector C_(h) 12 definedby two unit vectors a₁ 15 and a₂ 16; C_(h)=na₁+ma₂, where n and m areintegers and designated as the roll-up index (n, m) as shown in FIG. 1.The (n, m) and C_(h) have been referred to as -chiral index (or simply-chirality) and -chiral vector, respectively. A roll-up vector with m=014 results in zigzag nanotubes and a roll-up vector with n=m 13 givesarmchair nanotubes. For their electronic properties, armchair SWNTs havemetallic properties, and zigzag and chiral SWNTs are either metallic orsemiconducting, depending on the roll-up index (shown in FIG. 1). Whilearmchair and zigzag are achiral, a chiral SWNT has a pair of helicalisomers.

FIG. 2A illustrates an unfunctionalized semiconducting SWNT 17. As shownin FIG. 2B, the metallic SWNT 18 is selectively and covalentlyfunctionalized with an anionic group 19. In other example embodiments ofthe invention, the metallic SWNT can be selectively and non-covalentlyfunctionalized with anionic or cationic functional groups or molecules.

A continuous inkjet printing based SWNT separation system 28 is shown inFIGS. 3, 4 and 5. System 28 includes an ink reservoir 21 thatcontinuously pumps ink into a printhead 22, also called a liquidejector, to create a continuous stream, also referred to as a jet, ofink 29 from each of the nozzles 30 of the liquid ejector 22. Thestimulation controller 23 generates stimulation waveforms 37, patternsof time-varying electrical stimulation pulses, to cause a stream ofdrops to form from the jet beyond the outlet of each of the nozzles 30on printhead 22, described in more detail below. These stimulationpulses of the stimulation waveforms 37 are applied to stimulationdevice(s) 31, for example, a heater or piezoelectric device, associatedwith each of the nozzles 30 with appropriate amplitudes, and timings tocause drops 32 and 33 to break off from the continuous stream 29. Theprinthead 22 and deflection mechanism 24 work cooperatively in order todetermine whether ink droplets are deflected to a first collector 26,collector 1, or deflected to a second collector 27, collector 2, andrecycled via the ink recycling unit 25. The ink in the ink recyclingunit 25 is typically directed back into the ink reservoir 21. In otherexample embodiments of the invention, one or both of first collector 26and second collector 27 can be replaced with a receiver upon whicheither of drops 33 or drops 32, respectively, impinge or contact.

The ink is distributed under pressure to the back of the printhead 22 byan ink channel that includes a chamber or plenum formed in a substrate,for example, a silicon substrate. Alternatively, the chamber could beformed in a manifold piece to which a silicon substrate nozzle plate isattached. The ink preferably flows from the chamber through slots orholes etched through the silicon substrate of the printhead 22 to itsfront surface, where a plurality of nozzles and stimulation devices aresituated. The ink pressure suitable for optimal operation will depend ona number of factors, including geometry and thermal properties of thenozzles and thermal and fluid dynamic properties of the ink. Theconstant ink pressure can be achieved by applying pressure to inkreservoir 21 under the control of ink pressure regulator 20. Adeflection mechanism 24 includes electrostatic deflection components,described in more detail below.

The stimulation controller 23 includes one or more stimulation waveformsources 34 that generate drop formation waveforms 37 in response to theinput data and provide or apply the drop formation waveforms 37, alsocalled stimulation waveforms, to the drop formation device(s) 31associated with each nozzle 30 or liquid jet 29. In response to theenergy pulses of applied stimulation waveforms 37, the drop formationdevice 31 perturbs the continuous liquid stream 29, also called a liquidjet 29, to cause individual liquid drops to break off from the liquidstream. The drops break off from the liquid jet 29 at a break off lengthdistance, BL, from the nozzle plate.

It should be appreciated that different mechanical configurations ofcollector(s), receiver(s), or substrate(s) can be used. For example, inthe place of first collector 26, the collection drops enriched withfunctionalized nanotubes can be deposited and patterned directly on asubstrate 1 to form electrical traces, components, or devices, forexample, a field effect transistor, electrode, or capacitor.Alternatively, the drops enriched with non-functionalized nanotubes canbe selectively deposited onto a substrate, for example, substrate 1 orsubstrate 2, to form electrical traces, components, or devices, forexample, a field effect transistor, electrode, or capacitor. In theseexample embodiments of the invention, first collector 26, secondcollector 27, or both can be replaced a receiver or substrate. When thisis done, the substrate that replaces first collector 26 can be referredto as a first substrate while the substrate that replaces secondcollector 27 can be referred to as a second substrate. First substrate,second substrate, or both can be flexible or rigid. Substrate examplesinclude glass, plastics, laminates, or multilayered structures.Typically relative movement between system 28 occurs during printing.First substrate, second substrate, or both can be positioned on asubstrate transport that either moves or remains stationary duringprinting while system 28 either remains stationary or moves,respectively. Alternatively, both the substrate transport and the system28 can be in a complimentary fashion. As contemplated herein, thesubstrate and substrate transport themselves are conventional.

Drop forming pulses of the stimulation waveforms 37 are provided by thestimulation controller 23, and are typically voltage pulses sent to thedrop formation device(s) 31 of the printhead 22 through electricalconnectors, as is well-known in the art of signal transmission. However,other types of pulses, such as optical pulses, can be sent to the dropformation device(s) 31 of printhead 22 to cause collection and recycledrops to be formed at particular nozzles. For example, once formed, thecollection drops enriched with functionalized SWNTs travel to and arecollected by first collector 26, collector 1, while the recycle dropstravel to and are collected by second collector 27, collector 2, as willbe described.

Referring to FIGS. 4 and 5, the nanotubes separation system hasassociated with it, a printhead 22 that is operable to produce from anarray of nozzles 30 an array of liquid jets 29. As shown in FIGS. 4 and5, the arrays 29 and 30 extend into and out of each figure. Associatedwith each liquid jet 29 are a drop formation device 31 and a dropformation waveform source 34 that supplies a stimulation waveform 37,also called a drop formation waveform, to the drop formation transducer.The drop formation device 31, commonly called a drop formationtransducer or a stimulation transducer, can be of any type suitable forcreating a perturbation on the liquid jet including, for example, athermal device, a piezoelectric device, a MEMS actuator, anelectrohydrodynamic device, an optical device, an electrostrictivedevice, and combinations thereof.

In FIG. 5, liquid jet 29 breaks off into drops with a regular period atjet break off location 35, which is a distance BL from the nozzle 30.The distance between a pair of successive drops 36 produced at thefundamental frequency labeled 32 and 33 in FIG. 5 is equal to, orapproximates, the wavelength λ of the perturbation on the liquid jet.This sequence of drops breaking from the liquid jet forms a series ofdrop pairs 36 that includes a drop 32 and a drop 33. Each drop pairincludes a first drop and a second drop, one of which is a collectiondrop and one of which is a recycle drop. The terms first drop and seconddrop are not intended to indicate a time ordering of the creation of thedrops in a drop pair. The frequency of formation of a drop pair 36 iscommonly called the drop pair frequency f_(p), is given by f_(p)=f_(o)/2and the corresponding drop pair period is τ_(p)=2τ_(o).

The creation of the drops is associated with energy pulses supplied bythe drop formation device operating at the fundamental frequency f_(o)that creates drops having the same volume separated by the distance λ.It is to be understood that although in the example embodiments shown inFIGS. 4 and 5, the first and second drops have essentially the samevolume; the first and second drop can have different volumes such thatpairs of first and second drops are generated on an average at the dropformation frequency.

FIG. 5 also shows a charging device 38 including a charging electrode 39and charging voltage source 40. The charging voltage source 40 suppliesa charge electrode waveform 41 which controls the voltage signal appliedto the charge electrode. The charge electrode 39 associated with theliquid jet is positioned adjacent to the break off location 35 of theliquid jet 29. If a non-zero voltage is applied to the charge electrode39, an electric field is produced between the charge electrode and theelectrically grounded liquid jet. The capacitive coupling between thecharge electrode and the electrically grounded liquid jet attractsfunctionalized SWNTs carrying opposite charge (by design) to the end ofthe electrically conductive liquid jet. The liquid jet is groundedthrough contact with the liquid chamber of the grounded drop generator.This causes the end of the jet to have enrichment in the concentrationof functionalized SWNTs 18. This is illustrated in FIG. 6B using, by wayof example, a concentration of negatively charged functionalized SWNTs18 in the end portion of the jet when a positive voltage is applied tothe charge electrode 39. If the end portion of the liquid jet breaks offto form a drop while there is a net charge on the end of the liquid jet,the functionalized SWNTs in the end portion of the liquid jet at aconcentration higher than the average are trapped in the newly formeddrop 42. Thus, in FIG. 6B, the newly formed drop 42 is enriched innegatively charged functionalized SWNTs as compared to the feedsolution.

When the voltage level on the charge electrode is changed, the chargeinduced on the liquid jet changes due to the capacitive coupling betweenthe charge electrode and the liquid jet. Accordingly, the concentrationof the functionalized SWNTs on the newly formed drop can be controlledby varying the electric potential on the charge electrode. This isillustrated in FIG. 6A. When the voltage on the charge electrode iszero, the concentration of the functionalized and non-functionalizednanotubes in the newly formed drop 42 corresponds to that of the feedsolution.

Referring back to FIGS. 4 and 5, the voltage on the charging electrode39 (or charging electrodes 39 a and 39 b) is controlled by a chargingvoltage source 40 which provides a varying electrical potential in theform of a charge electrode waveform 41 between the charging electrode 44and the liquid jet 43. In embodiments utilizing the first collectiondrop selection technique, the charge electrode waveform 41 is usually atwo state waveform operating at the drop pair frequency equal tof_(p)=f_(o)/2, that is at half the fundamental frequency, orequivalently at a drop pair period τ_(p)=2τ_(o), that is twice thefundamental period. The charge electrode waveform 41 includes a firstdistinct voltage state and a second distinct voltage state, alsoreferred to as the recycle drop voltage state and the collection dropvoltage state, respectively. Each voltage state is usually active for atime interval equal to the fundamental period. In embodiments utilizingthe second collection drop selection technique, the charge electrodewaveform is a two state waveform operating at the fundamental frequencyf_(o) or equivalently at the fundamental period τ_(o), and each voltagestate is usually active for a time interval equal to half thefundamental period τ_(o)/2.

The charging device 38 is synchronized with the drop formation waveformsource 34 so that a fixed phase relationship is maintained between thecharge electrode waveform produced by the charging voltage source 40 andthe clock of the drop formation waveform source. This occurs because thecharge electrode waveform period is the same or an integer multiple ofthe period of the drop formation waveform applied to the drop formationtransducer. The phase relationship between drop formation waveforms andthe charge electrode waveforms is maintained even though the chargeelectrode waveform is independent of the image data supplied to the dropformation transducers. As a result, the phase of the break off of dropsfrom the liquid stream, produced by the drop formation waveforms, isphase locked to the charge electrode waveform. For example, inembodiments utilizing the first collection drop selection technique, thedrops 32 and 33 shown in FIGS. 4 and 5 are generated one fundamentalperiod τ_(o) apart in time so that they have different charge states.Collection drops are formed while the charge electrode is in thecollection drop voltage state and recycle drops are formed while thecharge electrode is in the recycle drop voltage state so that collectiondrops 32 are charged to a collection drop charge state and recycle drops33 are charged to a recycle drop charge state also called a firstrecycle drop charge state. The first recycle drop charge state isdistinct from the collection drop charge state.

Referring back to FIGS. 2, 4, 5, and 6B, the functionalized SWNTs areconsidered to be negatively charged and the collection drops 32 areconsidered as having a negative charge. In an alternate exampleembodiment using the opposite polarity of the two voltage states, thecollection drops can be positively charged rather than negativelycharged by attaching positively charged functional groups on the type ofSWNTs (metallic or semiconducting) to be enriched. Although one type of(either metallic or semiconducting) SWNTs are considered charged, it ispossible to attach functional groups of opposite polarities to metallicand semiconducting SWNTs so that the charge electrode voltage canalternate between collection drop voltage state and recycle drop voltagestate which are opposite in polarity.

In order to selectively collect collection drops in first collector 26,deflection electrodes 43 and 44 are utilized to attract the collectiondrops which are then sent to first collector 26. FIG. 4 shows anembodiment in which the deflection electrode 43 attracts collectiondrops carrying a negative charge traveling along the collection droppath 45. In this embodiment, the collection drop charge state induced onthe collection drop of the drop pair is distinct from the recycle dropcharge state induced on the recycle drops of the drop pair. Thecollection drops are highly charged and deflected to first collector 26while the recycle drops have a relatively low charge (or no charge) andare relatively undeflected and are allowed to reach second collector 27along the recycle drop path 46. If the recycle drops carry substantialcharge with opposite polarity as that of collection drops they aredeflected away from the appropriate deflection electrode and collectedby second collector 27. As shown in FIG. 4, second collector 27 ispositioned to collect recycle drops to facilitate recycling of the inkso that it can be jetted through the print head again. In this manner,the ink can be refined as many times as is desired.

FIG. 7 shows a block diagram outlining the steps to practice the methodof sorting SWNTs according to the various embodiments of the invention.Referring to FIG. 7, the method of sorting SWNTs begins with step 150.In step 150, pressurized liquid is provided under a pressure that issufficient to eject a liquid jet through a linear array of nozzles in aliquid chamber. Step 150 is followed by step 155.

In step 155, the liquid jets are modulated by providing drop formationdevices associated with each of the liquid jets with drop formationwaveforms that cause portions of the liquid jets to break off into aseries of collection drops or recycle drops. The drop formationwaveforms control one or more of the break off timing or phase relativeto the charging waveform applied to the charge electrode, the dropvelocity, and the size of the drop being formed to determine whether acollection drop or a recycle drop is formed. Step 155 is followed bystep 160.

In step 160, a common charging device is provided which is associatedwith the liquid jets. The common charging device includes a chargeelectrode and a charging voltage source. A charge electrode waveformwhich includes a first distinct voltage state and a second distinctvoltage state is applied to the charging voltage source which results ina varying electrical potential in the vicinity of drop break off fromthe jets. The first and second voltage states are also called collectiondrop voltage states and recycle drop voltage states respectively. Thecharge electrode waveform has a period equal to the minimum timeinterval between successive collection drops defined as the printperiod. Step 160 is followed by step 165.

In step 165, the charging device, the drop formation device aresynchronized so that the collection drop voltage state is active whencollection drops break off from the jets and the recycle drop voltagestate is active when recycle drops break off from the jets in all thenozzles in different groups. This produces a collection drop chargestate on collection drops and recycle drop charge states on recycledrops. Step 165 is followed by step 170.

In step 170, collection drops are deflected. Collection drops are thosedrops enriched with functionalized SWNTs. A deflection mechanismincludes an electrostatic deflection device which causes the collectionto begin traveling along a first trajectory and causes the recycle dropto begin traveling along a second trajectory, the first and secondtrajectories being different when compared to each other. Step 170 isfollowed by step 175.

In step 175, drops traveling along one of the first trajectory and thesecond trajectory are collected by a collector. These drops arecollection drops. Drops traveling along the other trajectory are allowedto be collected in a second collector for recycling.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention.

PARTS LIST

-   10 Single-Walled Carbon Nanotube (SWNT)-   11 Graphene Sheet-   12 Roll-Up Vector-   13 Armchair Roll-Up Vector-   14 Zigzag Roll-Up Vector-   15 Unit Vector a₁-   16 Unit Vector a₂-   17 Non-Functionalized Semiconducting SWNT-   18 Functionalized Metallic SWNT-   19 Anionic Functional Group-   20 Ink Pressure Regulator-   21 Ink Reservoir-   22 Printhead or Liquid Ejector-   23 Stimulation controller-   24 Deflection Mechanism-   25 Ink Recycling Unit-   26 Collector1-   27 Collector2-   28 Continuous Inkjet Printing Based SWNT Separation System-   29 Liquid Jet-   30 Nozzle-   31 Drop Formation Device-   32 First Drop-   33 Second Drop-   34 Drop Formation Waveform Source-   35 Drop Pair Merge Location-   36 Drop Pair-   37 Drop Stimulation Waveform-   38 Charging Device-   39 Charge electrode-   39 a Second Charge Electrode-   39 b Optional Symmetric Charge Electrode-   40 Charging Voltage Source-   41 Charge Electrode Waveform-   42 Newly formed Drop-   43 Deflection Electrode-   44 Optional Deflection Electrode-   45 Collection Drop Trajectory-   46 Recycle Drop Trajectory

1. A method of printing an electronic device comprising: providing asource of a mixture of semiconducting carbon nanotubes and metalliccarbon nanotubes in a carrier liquid; providing a printhead; providing asubstrate; separating the mixture of semiconducting carbon nanotubes andmetallic carbon nanotubes in the carrier liquid using the printhead; andcausing one of the separated semiconducting carbon nanotubes and theseparated metallic carbon nanotubes to contact the substrate inpredetermined pattern.
 2. The method of claim 1, wherein the printheadis a continuous inkjet type printhead.
 3. The method of claim 1, whereinone of the semiconducting carbon nanotubes and metallic carbon nanotubesis functionalized to carry a charge.
 4. The method of claim 3, whereinseparating the mixture of semiconducting carbon nanotubes and metalliccarbon nanotubes in the carrier liquid using the printhead includesusing an electrostatic force to concentrate the functionalized carbonnanotubes.